Information about the prevalence of balance/vestibular problems has been limited. There has been a lack of population-based information on prevalence, although it has been recognized that balance disorders, disequilibrium and dizziness from vestibular disturbance constitute a major public health problem. Epidemiologists and other scientific staff of NIDCD have collaborated with the National Center for Health Statistics (NCHS) on the development of questions and examinations for the assessment of balance problems in the US population. One of our first efforts was in development of questions for the 1994 and 1995 Disability Supplement to the National Health Interview Survey. Since hearing impairment and balance disorders are often linked, this survey included additional questions on tinnitus and other hearing impairments. Based on preliminary analyses for 1994 data, 4,675,000 adults in the US reported a balance problem lasting at least 3 months, and 44% were 65 years of age or older. We have also examined the question of dizziness lasting more than 3 months and found that it was mentioned less frequently than balance disorders among the elderly (about half as often among those aged 75 years or older). However, among younger adults, 18-24 years old, dizziness was the more common complaint. Subjects who reported both dizziness and balance problems were more likely to have had chronic tinnitus, other sensory problems (including problems with smell/taste and difficulty seeing), and were more frequently depressed. Those reporting balance problems (with or without dizziness) were more likely to experience limitations of activity and hearing problems compared to those reporting only dizziness. Women were more likely than men to report problems with balance, but race/ethnicity was not associated. In addition to this study, we have also collaborated with NCHS on the design of a balance component for the Fourth National Health and Nutrition Examination Survey (NHANES IV), 1999-2004. This survey began collecting household questionnaires and conducting examinations in April 1999. A modified Romberg test is being used in the mobile examination centers (MECs) to provide an objective measure of the subjects balance/vestibular performance. In addition, questionnaires relating to problems with balance are completed during household interviews prior to testing in the MECs. Similarly, our knowledge of disorders of the chemical senses has been quite limited. In the late 1970s, a consensus among experts convened by NIH was that more than 2 million adults in the U.S. had a disorder of smell or taste. A large, nonrandom survey conducted by the National Geographic Society in 1987 found that 1% of their 1.2 million respondents could not smell three or more of six odorants using a scratch and sniff test. Age was an important factor, with a decline beginning in the second decade of life. No comparable data has been available for taste, although it has been suggested that the sense of taste remains more robust with age. The Epidemiology Branch, NIDCD has collaborated with NCHS to acquire information on the prevalence of smell and/or taste problems using the Disability Supplement to the National Health Interview Survey (NHIS). Publication of preliminary results from this study, based on the 1994 data, occurred during the past year. We estimated a prevalence of 2.7 million (1.4%) adults in the US with a chronic olfactory (sense of smell) problem. In addition, we calculated that 1.1 million (0.6%) adults in the US had a chronic gustatory (taste) problem. When smell or taste problems were combined, 3.2 million (1.65%) adults in the U.S. were estimated to have a chronic chemosensory problem. The estimated prevalence rates increase markedly with age. Almost40% of adults with a chemosensory problem (1.5 million) were greater than 65 years of age. In a multivariate analysis, we found overall health status, othersensory impairments, functional limitations (including difficulty standing or bending), depression, phobia, and several other health-related characteristics were associated with an increase in the rate of chemosensory disorders. We have begun to explore the 1994 and 1995 Disability Supplement datasets jointly in order to extend the earlier analysis. With more subjects available, we will be able to evaluate additional risk factors for chemosensory problems.